The present invention relates to a lighting device for surface inspection used for the inspection of products etc in factories.
Lighting devices are employed for inspection of the external appearance and/or defects of products etc in factories. For such lighting devices, lighting devices of higher luminous intensity than that of ordinary lighting devices are often required; for these purposes, halogen lamps are often employed as the light source. Illumination of the subject of inspection is performed by directing the light emitted from a halogen lamp incorporated in the main device body of the lighting device onto one end of an optical fiber bundle comprising a plurality of optical fibers, and extracting this from the tip thereof.
However, although a halogen lamp has the advantage that high luminous intensity is obtained, the luminous intensity gradually decreases with time of use, due to evaporation etc of the filament, with the result that it becomes unusable usually after about 2000 hours. Thus, since the life of a halogen lamp is short, maintenance, involving replacement etc, must be carried out frequently and in addition, in cases where inspection with the same luminous intensity is required, since the luminous intensity gradually decreases with period of use, operation to maintain the same luminous intensity by constantly performing fine adjustment of the supplied voltage etc becomes necessary. Such maintenance or luminous intensity adjustment operations interfere with automation of the product inspection step and constitute a factor that adversely affects the inspection efficiency. Furthermore, owing to the characteristic of halogen lamps that their amount of light increases or decreases only slowly in response to turning the power source on or off, in cases where, depending on the type of inspection, it is required that the light should be turned on and off instantaneously in stroboscopic fashion, the method must be adopted of cutting off the light mechanically by means of a shutter or the like, leading to the drawback that the device becomes complicated and of large size. Also, since the halogen lamp itself is comparatively large, there is the inconvenience that making the main body of the device compact is difficult.
Although various devices have been considered in order to solve such inconveniences, it has not been possible to solve any of the above problems or solutions have been difficult to implement from the point of view of cost, so the development of a lighting device for inspection purposes that does not have these problems is desired.
An object of the present invention is to provide a lighting device whereby these problems are solved at a stroke and which basically adopts a construction wherein LEDs are respectively mounted at the light guide input terminals of optical fibers, and whereby an amount of light sufficient for inspection purposes can be supplied in stable fashion, and which has a long life.
In order to achieve this object, a lighting device according to the present invention for surface inspection is constituted such that light emitted from a light source is fed into the light guide input terminal of an optical fiber bundle obtained by bundling a plurality of optical fibers and is employed for illumination by being extracted from the light guide output terminal thereof, in which the light source comprises a plurality of LEDs and the light that is emitted from each of the LEDs is arranged to be respectively guided into one or more optical fibers.
By means of such a construction, since a plurality of LEDs are employed, and the light that is emitted from each of the LEDs is respectively introduced into each optical fiber (or two or more optical fibers), as a whole, luminous intensity that is fully sufficient for product inspection etc can be obtained by making the number of LEDs a large number. Furthermore, due to the characteristics of LEDs, compared with a halogen lamp, an amount of light that is much more stable can be maintained over a long period, making it possible to greatly reduce the work involved in maintenance and/or adjustment in order to maintain the luminous intensity level. Automation of the product inspection step can therefore be facilitated, and the efficiency of inspection can be raised.
Also, in order to simplify the construction and to reduce as far as possible the loss of light at the region of the junction of the optical fibers and the LEDs, it is desirable that the light guide input terminal of the optical fibers is directly bonded to the light-emitting element main bodies of the LEDs.
Also, specifically, as a preferred embodiment aimed at increasing the compactness and reducing the weight of the device, there may be mentioned a device wherein a plurality of light-emitting element main bodies that constitute the aforesaid LEDs are arranged so as to be distributed on the surface of a circuit board. The plurality of light-emitting element main bodies may be arranged distributed in matrix fashion on the surface of the printed circuit board.
When the light-emitting element main bodies are arranged distributed in this way on the printed circuit board, the amount of heat that is generated by the closely packed LEDs becomes large and tends to accumulate in the printed circuit board, so the amount of light emitted by the LEDs and their life may be reduced.
Accordingly, in order to efficiently remove this amount of heat, it is desirable to arrange a cooling device in the vicinity of said circuit board. Specifically, as such a cooling device, there may be provided a heat sink to the rear of the printed circuit board, or a Peltier element for cooling purposes may be adhered to the rear face of the circuit board. Furthermore, it is desirable to provide a heat-removing fan for introducing and circulating external atmosphere within the lighting device.
Also, in order to suppress generation of heat by the densely packed LEDs, it is desirable to provide a switch that turns on/off the supplied power of the light-emitting element main bodies. Specifically, a switch is desirable that is operated in pulse modulation mode. In this way, since the LEDs can be turned on/off in response to turning on/off of the supplied power in an extremely short time of the order of microseconds, it becomes possible to achieve a considerable reduction in the amount of heat generated by the densely packed LEDs, and, even in cases where, depending on the type of inspection, the light is required to be turned on/off instantaneously in stroboscopic fashion, this can be achieved simply by turning the power on/off, making it possible to meet such demands with an extremely simple construction.